i965: Stop advertising GL_MESA_ycbcr_texture.

i965: Stop advertising GL_MESA_ycbcr_texture.

The "new" fragment shader backend has never supported the necessary
color conversion code for this to work.  We began using the new backend
in Mesa 7.10 for GLSL (commit a81d423d93f22a948f3aa4bf73, October 2010),
and for ARB_fragment_program in Mesa 9.1 (commit 97615b2d8c7c3cea6fd3a4,
August 2012).

I haven't heard any complaints, so I don't think anyone will miss this
feature.  I believe mplayer used it at one point, but these days
defaults to other paths anyway.

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <idr@freedesktop.org>
Reviewed-by: Eric Anholt <eric@anholt.net>